Thermionic device for use with wave guides



Sept. 2 1948.

S. G. TOMLIN THERMIONIC DEVICE FOR USE-WITH WAVE GUIDES Filed Oct. 14, 1942 dEEaK l Z mveu'roa -26. EMU/v AJTORNEY Patented Sept. 28, 1948 THERMIONIC'DEVICE FOR USE WITH WAVE GUIDES Stanley Gordon Tomlin, London, England, assignor to Standard Telephones and Cables Limited, London, England, a British company Application October 14, 1942, Serial No. 462,027 In Great Britain August 29, 1941 8 Claims.

The present invention relates to electronic discharge apparatus for use with dielectric wave guides.

Dielectric guide systems of various kinds have been described in some detail heretofore in the papers on Hyperfrequency wave guides by J. R. Carson, Mead and Schelkunoff and by G. C. Southworth, appearing in the April 1936 issue of the Bell System Technical Journal. The dielectric guide itself has taken a wide variety of forms, but typical of guides disclosed heretofore is one consisting of a rod of dielectric material and another consisting essentially of a metallic pipe containing dielectric medium.

Dielectrically guided waves are capable of transmission in an indefinitely large number of forms or types, each type being distinguished by the characteristic spacial distribution and interrelation of the component electric and magnetic fields comprising the Waves. Although as already stated there are an indefinite number of types of dielectrically guided waves, they fall into either of two broad classes. In the one class, assuming now for the sake of simplicity that the guide is in the form of a metallic tube, the electric component of the wave is transverse to the tube and at no point does it have a longitudinal component excepting as the tube is not quite a perfect conductor. The magnetic component, on the other hands, has both transverse and longitudinal components. This class has been designated as transverse electric waves or TE waves. In the other class the magnetic component is transverse to the tube and at no point does it have a longitudinal component, but the electric component has in general both transverse and longitudinal components. This class has been designated as transverse magnetic waves or TM waves.

The various possible types of dielectrically guided waves in each of these two classes have been identified and distinguished from each other by their order and by their mode of propagation. The order of the wave is determined by the manner in which the field intensity varies circumferentially around the axis of the guide whereas the mode is determined by the manner of its variation with radial distance from the axis of the guide. The usual convention is herein adopted of designating a TE wave by I-Inm, where n represents the order and m the mode. larly, a TM wave of the nth order and mth mode will be represented by Enni- The object of the present invention is to provide arrangements for producing electrotmag netic waves of ultra short wave length in and for propagation along dielectric wave guides or for receiving and amplifying and detecting such waves.

Arrangements for producing ultra high frequencies are known which consist of a space resonator across which a beam of electrons is directed at a voltage antinode so as to be acted upon by the electric field within the chamber in order to bunch or group the electrons, and at another portion of the path the electrons give up a portion of their energy to the field to maintain oscillation. The velocity of the electrons, dimensions of the space resonator and positions along the electron path at which energy is absorbed and given up, being appropriately selected.

Electron discharge apparatus for use with dielectric wave guides according to the present invention comprises a length of wave guide having a reflector at one end whilst the electro- 7 magnetic waves may proceed through the other end, and means for producing and directing a beam of electrons across the guide in a direction parallel to the electric field lines of force of the electromagnetic waves and at a field antinode so as to be velocity modulated by said field and bunched.

In one embodiment of the invention, the beam of electrons after traversing the guide in one direction is reflected back from an electrode to Simiretraverse the guide and during the period between traversing the guide the electrons become bunched and on the second traversal feed energy.

to the guide.

In another embodiment, after the electrons have traversed the guide for the bunching operation, said electrons are arranged to strike a sec ondary electron emission electrode and the secondary electron beam thus generated is directed across the guide to give up energy to the guide.

In another embodiment, the guide is arranged to receive electromagnetic waves and to reflect said waves from said reflector to produce standing waves, and the velocity modulated and bunched beam of electrons is collected, the electrode potentials being such that the apparatus works on a curved part of the output current control voltage characteristic, whereby a rectified output of the received electromagnetic waves is obtained,

In another embodiment the guide is arranged to receive electromagnetic waves which are reflected from the reflector in the guide to produce standing waves within the guide and the electron beam is reflected back across the guide after potential of the electrode towards which the elec-- trons move after being velocity modulated are so adjusted that the apparatus works on a curved part of the output current-control voltage characteristic.

The invention will be better understood from.

the following description taken in conjunction with the accompanying drawingsyin which Fig. 1 shows schematically a planyiew of one.-

practical embodiment;

Fig. 1A shows an end view of the arrangement continuous line within the guide and equipotential lines are shown in broken line;

Fig. *3 shows the electric field distribution of an E11 wave in a guide of rectangular section;

Fig.4 shows the electric field distribution of an E01 wave in a guide-of circular section;

Fig. 5 shows diagrammatically a plan view of another embodiment.

Fig. 6 shows a modified form of the apparatus shownin Fig. 1 for use as a receiving arrangement with a wave guide system;

Fig. 7 is an end view of-the arrangement shown in Fig. 6.

The invention will be described in terms of wave guides of rectangular section ince the electromagnetic fields which can exist in these guides are somewhat simpler than in tubes of any other section. It is, however, to be understood that the use of guides'of other sections, particularly of circular section is envisaged and that guides of rectangular section are described by way of illustration only.

Referring to Fig. '1, an Hm waveis excited in a guide I of rectangular section by projecting a beam of electrons produced by an electric gun shown as cathode K and concentratinggridG through the wave guide-i at a voltage or electric.

field antinode, in a direction parallel to the electric fieldxand then refiectingrthe beam fromia low potential electrode. A back through'the wave guide I.

cathode K of the electron .gun nearly all electrons-will be reflectedand bunching'will occur since the'electron beam is velocity-modulated on its forward journey. If nowthe transit time to and from the reflector A is suitably adjusted the bunches which are formed, will pass across the guide at such time as the electric field is able to absorb energy from them so that oscillationsmay" lected by the reflector A whereas those electrons" which have lost energy on passing through the guide will be reflected and pass through-it a second time and if transit times are suitably ad justed this second passage will occur when the direction of the electric field in the Wave guide If the reflecting electrode A. has a'isufiieiciently negative potential with respectto the is such as to absorb energyjrom them. In this.

case the transit time from the modulating gap 4 0 to the reflector A and back to the gap should be (n+ periods, n-being an integer.

A third method of operation results from running the electrode A at a potential positive with respect to the cathode K in which case secondary elec'tron emission may-occur from the electrode A. If the potential of A is suitably adjusted the fast primary electrons striking A cause more secondary-electrons to be emitted than the slow :ones'so that'bunches of secondary electrons leave therelectrode A and pass across the modulating gap 0 giving up energy to the wave guide providedtransitztimes-are suitably adjusted. It is necessarythat the. transit time from the modulating' gap 0 to the secondary electron emitter A and sbaclctoi thel'gap. should be 12 periods, An alternativeZaction involving secondary emission arises if the distance from gap E] to the secondary electron emitter A is such that the primary electrons after velocity modulation, arrive in bunches at the secondary electron emitting surface. Then bunches of secondary eiectronswill leave the surface and on passing across the modulating gap 0 will give up energy to the guide,.again provided that transit times are: suitably adjusted.

In Fig.1 essential details of the apparatus are shown diagrammaticallyl. The wave guide I is a copper boxcof rectangularsection which maybe closed at "oneiendto'nly'Lthepther end being open as regards the electromagneticwaves to radiate I energy-therefromnTo produce a voltage or field antinode in the wave guide. one endis closed by a movableipiston P whichrreflects the waves in. cident thereon to producenstanding waves. In theien'drleft open, adiaphragm' D is necessaly in orderxto reduce the radiation damping which may otherwise .be excessive; 'Since the critical waveleng-thrfor'the wave guide-is twice the long side L of. the rectangular section Fig. 1A, this dimen-- .sion mustwbegreater than half the-wavelength to-.be-generated;: The short side of the rectangle shouldabe made as ilargeas possible since the:

losses-in the--g-uidaincrease rapidly as this dimensiona decreases. This dimension .cannot be .too-great. however because the fins F which have tobe-..intr.oduc.ed to make-the modulation gap 9 of sucha size: that thedtransit time of electrons crossing it'shouldbesmalLcompared with a period of -theloscillation, willhavea great. effect upon 1 the..characteristics. of .the. guide; For .a given value .of .theLlength, of,v the short. side a, andthe,

wavelength K the optimum value. of b, the length of thelong .side of the. rectangle, is given by provided :21). si-ik.

Another '1' method. of adjustment consists of compressing the-guideiso that themodulating gap width is altered; since thisvaries the capacitive-loading due -to the presence of the fins F.

The: position-of the :aperture through which the electron. beam 'is. projected is at a voltage or electric field. antinode and should therefore be atan oddenumber. .of quater wavelengths from' the..clos.ed .endP or aneven'number from an open end llas regards the waves, this wavelength being the wavelength. A inethe guide. which difiers from that .in..free space. To -reduce losses the. total length. of the guide. hetweenthe aperture .Q and the refiectingend Pshould be a minimum.. Since for small wavelengths the size of the apertureQ 1s limited,;for.it cannot be much longer than 4; withany advantagadt may be desirable to have several apertures and cathodes.

In order to obtain a sufficiently intense beam of electrons it may be advantageous to mount the apparatus between the poles of a magnet NS as shown in Fig. 1 producing a field along the path of the beam.

In Fig. 2B the electric field distribution of the H01 wave is shown. Since the equipotential surfaces of this field are planes parallel to the side of the wave guide which determines its critical wave length, thev introduction of a perfectly conducting plane M, Figures 2 and 2A, into the guide in this position would not alter the field field distribution. Suppose this to be done and further suppose that a metal tube T is mounted on this plate M as shown in Figs. 2 and 2A. Now

consider a beam of electrons projected across the guide through the metal tube T. The electrons will be velocity modulated at the first gap assuming that a high frequency field already exists, and in traversing the metal tube T will become bunched so that if the transit time through the tube is suitably adjusted energy will be given up to the electromagnetic field at the second gap 02 and so maintain the oscillations.

In the known coaxial line type of resonator the electric fields across the gaps between the inner and outer conductors are at any instant opposite to one another whereas in the type of oscillator shown in Fig. 2 these fields are in the same direction. It follows then that the transit time through the drift tube T must differ in this case by half a period from the value appropriate to the coaxial line resonator. A transit time of either or 1% periods is therefore necessary for this type of Wave guide oscillator. More generally the transit time through the drift tube V of the E11 wave and in a rectangular guide tube,

in Fig. 4 the electric field distribution of the E01 wave of a circular guide tube. .It is clear from these diagrams that these waves could be excited in the appropriate guides in a manner exactly analogous to the excitation of the coaxial line resonator. Further since the field strength at the centre of the tube is zero it might be possible to dispense entirely with any fin, or drift tube system inside the wave guide.

In another arrangement for exciting Ho,1 waves in a rectangular wave guide a beam of electrons is projected across the wave guide parallel to the lines of electric force and at an antinode of the electric field. It is known that if the transit time of electrons crossing the field in the giude is (n+ A) cycles of the oscillation to be excited, the system has a negative impedance and may therefore absorb energy from the beam thus maintaining the oscillating electromagnetic field. The structure of the apparatus is similar to that shown in Fig. 1, except that fins F may not be necessary since the gap width must now be much larger, preferably such as to make the transit time across it 1% periods of the required oscillation. The electron beam is finally collected on an electrode A maintained at the lowest possible potential consistent with collecting the whole of the beam.

A receiving arrangement according to the invention now to be described with reference to Figs, 6 and 7, is a straight forward detector.

Figs. 6 and '7 are similar to Figs. 1 and 2, the same references are given to like parts. The wave guide is open at one end which may be terminated in an electromagnetic horn M to increase the high frequency energy picked up by the wave guide. A beam of electrons is projected across the wave guide past a modulating gap across which the transit time is small compared with a period of the oscillation to be received, this gap being at an antinode of the electric field. The incoming signal thus velocity modulates an electron beam. Beyond the modulating gap is placed an auxiliary grid structure GI maintained at approximately cathode potential and beyond this is the collector electrode A maintained at a potential, positive with respect to the cathode K. By biasing the auxiliary control grid GI to a curved part of the collector current-grid voltage characteristic a rectified output is obtained in a manner analogous to triode anode bend detection.

Alternatively the auxiliary grid GI may be omitted and then if the collector electrode A is biased to a curved part of the collector currentcollector voltage characteristic detection results as before, the detected output being taken from the collector electrode A. If the spacing between modulating gap and auxiliary grid GI (or collector whenthis grid is omitted) is suitably adjusted electrons which are reflected back through the modulating gap may cause the wave guide to oscillate and since this oscillation may be in synchronism with the incoming carrier the detected output can be in creased.

The apparatus illustrated in Figs. 6 and 7 can also be used as an autodyne frequency changer. In this case it may be necessary to have a diaphragm D at the neck of the horn in order to reducev radiation damping for the oscillations have to be produced by refiection of the electron beam from the auxiliary grid GI. The piston P is adjusted to produce standing waves corresponding to a frequency differing by the required 1 intermediate frequenc from that of the carrier which it is desired to receive. Then by adjustment of the beam velocity so that the necessary transit times are obtained the arrangement is set into oscillation by reflection of electrons from the auxiliary grid (or collector if this grid is omitted) which is maintained at approximately cathode potential at a point in the curved part of the collector current-grid voltage (or collector voltage in the absence of a grid) characteristic. If the intermediate frequency chosen is not too high the wave guide will be only slightly out of adjustment for the carrier and thus two fields of slightly different frequencies will exist in the wave guide so that the electric field across the modulating gap will be of the form A cos wlt+B cos wzi. Then owing to the non-linearity of the collector electrode current characteristic the collector electrode current will have an intermediate frequency component of the form I cos (w1w2) t.

An improvement on the autodyne frequency changer hereinbefore described may be obtained as shown in Fig. 5 by providing two wave guides 1,2 side by' side across both of which an electron beam is projected at voltage antinodes. One of these guides I having an open end, with or with" out an electromagnetic horn, is adjusted to the incident carrier Wave frequency and the second 2 is'adjusted to the frequency of a local oscillator.

OS with which it is directly coupled. In this way the beam is velocity modulated by voltages A cos wit and B cos wzt in series and again as a result .ofathe :nonslinea'rityloithecollector electrode -voltage=output= current characteristic an .output current ;of-.the forml cos (mewzltis obtained.

. Alternatively. instead ,of..usin g;a separate local oscillator. the second wave guide .may be .set in oscillation by reflection .of ".BIGGISIZOIIS' from an auxiliarygr-idsuch as G! in Figsafi and 7.

-Whatisclaimed is:

v .1. Electron :discharge. ,appara'tusefor .use with rdielectric wave. guides comprising a lengthsofrthe wave 1 guideopen at 20118. end i a source of electrozm-agnetic waves coupled ,to rsaidppen end, are- .flectoracting :as a :closureat1-theother end, means for producingstanding waves insaid-guida means for-producing and directing abeam of electrons "transverselyacross the-,guideat a:pointralongthe guide wherea field ant-inode eXist-sandwherethe direction :of the electron beam ;is parallel to the ele ctric. field lines ,of. force; of the. electroma neti waves whereby the electron-sin said-beam: are ve-, locity --modulated byzsaid, field and: bunched in their passage acrossrthe 1 guide there :being openings transversely through "said, guide for thepassagetof sai'dibeam; means: for bringing: electrostatic charges to :bearwon said beam 'after passage,

through the guide and means tolimitztherspace acrossisai'd guide .to :atleastcne. gap within which the :electronszreact with said 'i field, 'so'zthat the transititime of electrons?crossing'saidrgapjs small compared with etherperiodofcscillations.

.2JE1ectron discharge (apparatus as claimed in claim 1 wherein the means for bringing an electrostaticchargefito bear onsaid -beam comprises a reflector electrode whereby the said 'beam 'of electrons-after traversing the guideu'n one .rdirection is reflected back to retraverse the guiderand wherel in the saidmeans ior limiting thehspace across "said guide to at'lea-st one gap comprises fins within said guide adjacent said openings. and parallel the guide and the velocity modulated and bunched'beam'o'f electrons iscollected-said means for bringing electrostatic charges to beargon' said beam being electrode-s whose potentials are such that'the apparatus works on a curved part of the output current versus control-voltage characteristic whereby "a rectified output'of the "received electromagnetic waves is obtained.

4; Electron dischangeapparatus as claimed in claim hwherein said means for bringing electro- 7 static chargesto bear on said beam comprising a collecting electrode spaced fromithewave guide at the end of the beam'path remote from 'thebe'am generating means "and an auxiliary grid provided between the collecting electrode and-the wall 'of' the wave guide and'thepotentials-on said electrodes are adjusted so that the apparatus 'works on the-curved partof the collector current-auxiliary grid voltage characteristic wherebyarectified output. of electromagnetic waves received along said guide is obtained.

.5. Electron discharge apparatus as claimed in claim 1 Whereinsaid means :for bringingrelectrostaticrch-argesixto bear; onisaid beam comprising a collectingelectroderspacedfromthe Wave guideat' 7 the end of :the beam-:pathremote from :the beam generating-means andithe :Width ;.of::the pat-h tra- ZAE 0,02 6

versed by .the electrons between the..'Wfl11. Ofi-th8 :Wave guide-and .the. collecting electrojdeis so adiustedand the potential of thesaidflcollecting electrode isso adjusted that part oftheelectrons are reflected back across the guide andgive up energyto the said electromagnetic wavesreceived along said guide whereby the detected output is amplified.

.finElectron discharge apparatus asclaimed in claim 1 wherein the guidels arrangedto receive electromagnetic waves whichreflected fromsaid nreflec-tor produce standing waves within the. guide,

-,'and-.said means for bringing electrostaticcharges Ito-bearon said beam comprising arefiectingelec- ;trode spaced from the waveguide attheen'dlof the beam-path remote from the beam regeneratingmeans whereby the electron-beam isrefiected back-across the guide afterbeingvelocitymodul-ated so as to give up energy to said.guide,..the

said reflector in said guide being sopositioned that the reflected beam produces cscillationsin said guide diiT-ering in frequency from-thereceived waves by a desired intermediate frequency, the potential of the said reflecting electrodebeso adjusted that the apparatus. workson a I curvedpart of the. output current-reflecting electrode voltage characteristic.

.7. Electron discharge apparatus as claimed .in .claim 1 for producing'Hoi electromagnetic waves wherein the said means tolimit the. space across theguide to at least onegap comprises-ametal .tube support-ed by a conducting plane sheetarranged parallel to the equ-ipotenti-al lines in. the

..guide, arranged with its longitudinal axistransversely of the guide so that theb-ea-m of electrons passes .therethroughand leaving gaps betweenthe .ends of said tube and the guide-wal1s,.:the.transit .time of the electronsand the dimensions .of said metal tube'being so adjusted .that in crossing the .filtstgap their path theelectrons absorb energy from the field andgive up energy to thefield at from said reflector to produce-standing waves in 1 the sec-0nd gap. 8. Electron discharge apparatus as-claimed in claim 1 wherein the transit time of the electrons crossing the field in the guide is arranged-to .be

.(n-l-MQ cycles of the oscillation to be -excited where n is an integer.

STANLEY GORDON TOMLIN.

file of this patent:

UNITED STATES PATENTS Number Name Date I .-j2,170,219 Seller Aug-22,1939 2,190,511 Cage Feb.13,' 1940 2,190,515 Hahn ,Feb. 13,- c1940 2,207,846 Wolf July 16; 1'940 2,220,841 Metcalf Nov; 15, 1940 2,223,082 "Van Mierlo Nov. 26, .1940 1 12,253,589 Southworth Aug. 26,1941 :2,293, 151 'Linder Aug; 18,1942 --2;320,860 F'remlin June 1,1943 2,367,295 Llewellyn .J an. 16,21945 2,368,031 Llewellyn :Jan. 23,1945 2,372,193 Fisk v.Mar. 27,;1945

FOREIGN PATENTS Number Country Date 541,631 Great Britain Dec.; 4,. 1941 543,400 Great Britain Feb. .24; .1942

Certificate of Correction Patent N 0. 2,450,026 September 28, 1948 STANLEY GORDON TOMLIN It is hereby certified that errors appear in the above numbered patent requiring correction as follows:

In the grant, line 14, strike out the words of seventeen years; same line, after grant insert until August 2.9, 1961; in the heading to the printed specification, line 9, before 8 Claims insert the following Section 1, Public Law 690, August 8, 1946. Patent expires August 2.9, 1.961;

and that the said Letters Patent should be read with these corrections therein that the same may conform to the record of the case in the Patent Office.

Signed and sealed this 21st day of Februar A. D. 1950.

THOMAS F. MURPHY,

Assistant Oommz'ssz'oner of Patents. 

